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Abstract

Obstructive sleep apnea (OSA) is one of the most common sleep disorders. It is characterized by repetitive obstruction of the upper airways during sleep. The frequency of such events can range up to hundreds of events per sleep-hour. Full closure of the airways is termed apnea, and a partial closure is known as hypopnea. The number of apnea/hypopnea events per hour is known as the AHI-index, and is used by clinical community as a measure of the severity of OSA. OSA, when untreated, presents as a major public health concern throughout the world. OSA patients use health facilities at twice the average rate (Delaive, Roos, Manfreda, & Kryger, 1998), causing huge pressures on national healthcare systems. OSA is associated with serious complications such as cardiovascular disease, stroke, (Barber & Quan, 2002; Kryger, 2000,), and sexual impotence. It also causes cognitive deficiencies, low IQ in children, fatigue, and accidents. Australian Sleep Association reported (ASA, 1999) that in the state of New South Wales alone 11,000–43,000 traffic accidents per year were attributable to untreated-OSA.

Background

Definition of Sleep Apnea and Hypopnea

Sleep apnea refers to a cessation of breathing at night, usually temporary in nature. The American Academy of Sleep Medicine Task Force formally defines apnea as:

a.

Cessation of airflow for a duration ≥10s, or

b.

Cessation of airflow for a duration < 10s (for at least one respiratory cycle) with an accompanying drop in blood oxygen saturation by at least 3%.

Hypopnea is defined as a clear decrease (≥50%) in amplitude from base line of a valid measure of breathing (eg., airflow, air pressure) during sleep for a duration ≥10s, plus either:

a.

An oxygen desaturation of ≥3%, or

b.

An EEG-arousal (EEGA) (Flemons & Buysse, 1999).

The average number of obstructive sleep apnea and hypopnea events per hour of sleep, as computed over the total sleep period, is defined as the Apnea Hypopnea Index (AHI).

The Current Standards in Apnea/Hypopnea Diagnosis

The current standard of diagnosis of OSA is Polysomnography (PSG). Routine PSG requires that the patients sleep for a night in a hospital Sleep Laboratory, under video observation. In a typical PSG session, signals/parameters such as ECG, EEG, EMG, EOG, nasal/oral airflow, respiratory effort, body positions, body movements, and the blood oxygen saturation are carefully monitored. Altogether, a PSG test involves over 15 channels of measurements requiring physical contact with the patient.